$$\frac{n}{n-y}=\frac{2}{m+y}$$
$m=-y-\frac{2y}{n}+2$
$n\neq y\text{ and }n\neq 0$
$\left\{\begin{matrix}n=-\frac{2y}{y+m-2}\text{, }&y\neq -m\text{ and }y\neq 0\text{ and }y\neq 2-m\\n\neq 0\text{, }&m=2\text{ and }y=0\end{matrix}\right.$
